Optical arrangement for symmetrizing the radiation of two-dimensional arrays of laser diodes

ABSTRACT

An optical arrangement for symmetrizing beams which includes a plurality of laser diodes arranged next to one another. The plurality of laser diodes emit beams which are asymmetrical relative to a first direction and a second direction, with the second direction being perpendicular to the first direction. A microcylinder lens optics is arranged in an inclined manner around an optical axis. The beams emitted by the laser diodes in the first direction are collimated and deflected at different angles and are separated thereby. A direction element is arranged downstream of the microcylinder lens optics. The direction element deflects a beam of each individual laser diode in the second direction, whereby each of these beams is deflected by a different angle in the second direction, in such a way that central points of the individual beams converge at a predetermined distance in the second direction. The direction element deflects a beam of the individual laser diode in the first direction in such a way that each of these beams converges at a predetermined distance in the first direction. A redirection element is arranged at a predetermined distance downstream of the direction element. The redirection element compensates for different angles of deflection of the beams which are transmitted through the direction element in a plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage Application of InternationalApplication No. PCT/EP00/02708, filed Mar. 28, 2000. Further, thepresent application claims priority, under 35 U.S.C. §119, of GermanPatent Application No. 199 14 755.8 filed on Mar. 31, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an optical arrangement for symmetrizing thebeams from laser diodes.

2. Discussion of Background Information

For the production of high-power laser diode arrangements, a pluralityof laser diodes are arranged next to one another in a fixed orientationrelative to so-called laser diode bars. Such bars achieve optical outputof up to approximately 40W and comprise individual emitters arranged ina row with typical dimensions of the radiating surface from 50 μm×1 μmto 200 μm×1 μm, with the linear arrangement of these emitters alwaysoccurring in the direction of their greatest expansion. In order toachieve even greater outputs, such laser diode bars are stacked on topof one another in the direction of the smaller extension of the emittersinto laser diode stacks. The emission of these stacks is extremelyasymmetrical and has a low radiance due to the non-radiating regionsbetween the individual emitters of a bar and among the bars as comparedto the individual emitters.

In order to achieve a symmetrical bundle with the greatest possibleradiance as is needed, for example, for material processing or forpumping of solid state lasers, optical systems are necessary that, onthe one hand, cause a symmetrizing of the beams as well as a fading-outof the non-radiating regions for the purpose of maintaining theradiance.

Arrangements for symmetrizing laser diode stacks are known, for example,for connection to optical fibers and/or focusing in a focal spot. Here,depending on the requirements with regard to symmetrizing and radiance,different concepts are prior art.

The coupling of a stack is described in DE 195 00 513 C1. Here, it isdisadvantageous that the minimum distance between the individual bars isthree times the thickness of the collimation lenses, which may obstructthe integration of as great as possible a number of bars for a givenheight.

While an arrangement according to DE 195 44 488 does allow a scaling tovery high outputs by using many bars, the radiance achieved is at leastone order of magnitude less than the fiber-coupled laser diode bars,such as those according to DE 44 38 368.

Moreover, an optical arrangement of multiple laser diodes arranged nextto one another in a fixed allocation for symmetrizing of beams is known(DE 196 45 150 A1). The symmetrizing arrangement here comprises acylinder lens rotated around the optical axis, a directional lens fordeflecting the radiation beams of the individual laser diodes, aredirection lens for compensating the deflection of the directionallens, and a subsequent collimation lens.

SUMMARY OF THE INVENTION

The invention provides for an optical arrangement for symmetrizing thebeam of a scaleable number of laser diode bars that comprisesmicro-optic components that are comparably simple to produce, isaccessible to a cost-effective miniaturization, and with which thelosses in radiance accompanying the symmetrizing are as small aspossible. In particular, an improvement of the radiance should beattained as compared to fiber-coupled laser diode bars.

According to one non-limiting aspect of the invention, there is providedan optical arrangement for symmetrizing beams which includes a pluralityof laser diodes arranged next to one another. The plurality of laserdiodes emit beams which are asymmetrical relative to a first directionand a second direction. The second direction is perpendicular to thefirst direction. A microcylinder lens optics is arranged in an inclinedmanner around an optical axis. The beams emitted by the laser diodes inthe first direction are collimated and deflected with different anglesand are separated thereby. A direction element is arranged downstream ofthe microcylinder lens optics. The direction element deflects a beam ofeach individual laser diode in the second direction, whereby each ofthese beams is deflected by a different angle in the second direction,in such a way that central points of the individual beams converge at apredetermined distance in the second direction. The direction elementdeflects a beam of the individual laser diode in the first direction insuch a way that each of these beams converges at a predetermineddistance in the first direction. A redirection element is arranged at adistance downstream of the direction element. The redirection elementcompensates for different angles of deflection of the beams which aresent through the direction element in a plane.

The plurality of laser diodes may be arranged at least one of one abovethe other and on a common plane. The plurality of laser diodes may bearranged in a fixed location. The plurality of laser diodes nay bearranged to form a laser diode stack. The optical axis may correspond toan assigned linear array of laser diodes. The microcylinder lens opticsmay comprise a plurality of microcylinder lenses. The microcylinder lensoptics may have sufficient isoplanacy. The redirection element maycompensate for different angles of deflection of the beams which aresent through the direction element in a plane defined by the seconddirection and the optical axis. The first direction may define an “y”axis, the second direction may define an “x” axis, and the optical axisdefines a “z” axis. The redirection element may compensate for differentangles of deflection of the beams which are sent through the directionelement in a plane defined by an x-z plane.

The arrangement may further comprise at least one projection lensarranged between the direction element and the redirection element,whereby the at least one projection lens directs the beams in the seconddirection to a common focal spot. The arrangement may further compriseat least one optical fiber arranged at the common focal spot. The atleast one optical fiber may comprise one of a plurality of opticalfibers and a fiber bundle. The microcylinder lens optics may comprise aplurality of microcylinder lenses, at least one of the pluralitycomprising one of a gradient optical microcylinder lens, a sphericalmicrocylinder lens, an aspherical microcylinder lens, and a Fresnellens. The microcylinder lens optics may comprise a plurality ofmicrocylinder lenses, each the plurality comprising at least one of agradient optical microcylinder lens, a spherical microcylinder lens, aaspherical microcylinder lens, and a Fresnel lens. The direction elementmay comprise at least one of a doublet lens, a biconvex lens, and aplanoconvex lens. The direction element may comprise spherical surfaces.The direction element may comprise aspherical surfaces.

The arrangement may further comprise an optical element arrangedadjacent the direction element. The optical element may evenly deflectthe beams in the second direction in such a way that the beams in firstdirection are separated from one another at a predetermined distance inthe second direction. The optical element may comprise at least one ofan array of blazed gratings, a prism stack, and a mirror stack. Theoptical element may deflect the beams in the second direction bysectioning the direction element and subsequently joining the sectionssuch that they are displaced relative to one another in the seconddirection. The redirection element may comprise at least one of an arrayof blazed gratings, a prism stack, and a mirror stack.

The arrangement may further comprise a deflecting element arrangedbetween the direction element and the redirection element. Thedeflecting element may be arranged adjacent the redirection element,whereby the deflecting element deflects beams in the first direction insuch a way that they leave the redirection element parallel to theoptical axis. The deflecting element may comprise at least one of anarray of blazed gratings, a prism stack, and a mirror stack. Thedeflecting element may comprise a diffraction element. The redirectionelement may comprise a diffraction element.

The arrangement may further comprise a lens located between thedirection element and the redirection element, whereby the lens causes acollimation of individual beams in the second direction. The lens may belocated adjacent the redirection element and may comprise at least oneof a doublet lens, a biconvex lens, and a planoconvex lens. Thedirection element may comprise spherical surfaces. The direction elementmay comprise aspherical surfaces.

The arrangement may further comprise a focusing lens arranged downstreamof the redirection element, whereby the focusing lens focuses the beamsinto one or more focus spots or points. The focusing lens may compriseat least one of an achromate lens, an achromate and a meniscus lens, aplanoconvex lens, a planoconvex lens, a meniscus lens, and a biconvexlens. The focusing lens may comprise a spherical profile form. Thefocusing lens may comprise an aspherical profile form.

The invention may also provide for an optical arrangement forsymmetrizing beams comprising a plurality of laser diodes arranged toform an array. A plurality of microcylinder lenses is arranged adjacentthe array. A direction element is arranged downstream of the pluralityof microcylinder lenses. The direction element deflects some beams in an“x” direction, whereby each of these beams is deflected by a differentangle in the “x” direction, in such a way that central points ofindividual beams converge at a predetermined distance in the “x”direction. The direction element deflects some beams in a “y” directionin such a way that each of these beams converges at a predetermineddistance in the “y” direction. A redirection element is arranged at adistance downstream the direction element. The redirection elementcompensates for different angles of deflection of the beams which aresent through the direction element.

The invention can also provide for an optical arrangement forsymmetrizing beams comprising a plurality of laser diodes arranged toform an array. A plurality of microcylinder lenses is arranged adjacentthe array. A direction element is arranged downstream of themicrocylinder lenses. The direction element deflects some beams in asecond direction, whereby each of these beams is deflected by adifferent angle in the second direction, in such a way that centralpoints of individual beams converge at a predetermined distance in thesecond direction. The direction element deflects some beams in the firstdirection in such a way that each of these beams converges at apredetermined distance in the first direction. A redirection element isarranged at a distance downstream the direction element. At least onelens is arranged adjacent the redirection element. At least one opticalfiber is arranged downstream the redirection element and the at leastone lens. At least some of the beams exiting the redirection element aredirected to a common focal spot on the at least one optical fiber.

Using a microcylinder lens that is assigned to each individual bar andinclined to its optical axis (z-axis), the beams emitted by theindividual emitter of each bar in the direction of the stack of thelaser diode bars is collimated, differently deflected, and thusseparated. This deflection occurs such that the centers of the beams ofindividual emitters of different bars lying above one another impact aredirection element at the same height in this direction at apredetermined distance. A direction element located downstream from themicrocylinder lenses causes a deflection of the beams of the individualemitters of a bar in the direction of the linear arrangement of theindividual emitter such that the beam centers of the emitters of one baroccur at a predetermined distance on the redirection element in thisdirection. Moreover, the direction element deflects the beam centers ofthe individual bars in the direction of the stack such that all centersin the stack direction also fall on the redirection element. Theredirection element deflects the emission beams originating from theindividual emitters such that the deflection angles produced by thedirection element are compensated again. A projection lens adjacent tothe redirection element projects the beams of each bar in a focal spot,located at a predetermined distance. These focal spots are coupled intothe face surfaces positioned there of the spread fibers of an opticalfiber bundle. This bundle causes the focal spots, which were originallyarranged one above the other in the direction of the stacking of thebars, to be rearranged into the desired symmetrical total focal spot.

By way of the multiple use of the direction and redirection element andthe projection lens for all bars, the arrangement thus described allowsa simple and cost-effective symmetrizing of the radiation from laserdiode stacks while maintaining the radiance of the individual emittersto the greatest extent possible.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention is shown in thedrawings and is explained in greater detail in the description below, inwhich:

FIG. 1 shows, from an X-Z orientation, the optical arrangement forsymmetrizing the beams of a two-dimensional array of laser diodes usinga fiber bundle;

FIG. 2 shows, from an Y-Z orientation, the optical arrangement forsymmetrizing the beams of a two-dimensional array of laser diodes usinga fiber bundle;

FIGS. 3a-5 a show, from an X-Z orientation, various embodiments of theoptical arrangement for symmetrizing the beams of a two-dimensionalarray of laser diodes using additional deflecting elements; and

FIGS. 3b-5 b show, from an Y-Z orientation, various embodiments of theoptical arrangement for symmetrizing the beams of a two-dimensionalarray of laser diodes using additional deflecting elements.

DETAILED DESCRIPTION OF THE INVENTION

In the optical arrangement shown in FIGS. 1 and 2, reference numbers 1a, 1 b, 1 c indicate three laser diode bars stacked in the y direction,where the limitation to (i.e., illustration of) three bars 1 a, 1 b, 1 cis solely for the purpose of an improved depiction. Each of these bars 1a, 1 b, 1 c comprises a plurality of individual emitters arranged in thex direction; for the sake of simplicity, only the two outer emitters andthe center emitter are shown here. The divergence of the beams of eachemitter is relatively large in the y-z plane (fast axis), the half angleof beam spread is 30° or greater. In the x-z plane (slow axis), on theother hand, the divergence of the beams of each emitter is comparativelylow. Here, the half angle of beam spread is typically approximately 6°.The total extension of the bars 1 a, 1 b, 1 c in the slow axis istypically 10 mm. The stack distance of the bars 1 a, 1 b, 1 c from oneanother is in the range of approximately 0.1 to several millimeters.

A microcylinder lens 2 a, 2 b, 2 c is assigned downstream of each of theindividual bars 1 a, 1 b, 1 c. In the path of the beams, a directionelement 3 and a lens 4, a redirection element 5 and another lens 6 aswell as optical fibers 7 a, 7 b, 7 c joined into an optical cable bundle7 follow in the sequence.

The microcylinder lenses 2 a, 2 b, 2 c, which are inclined relative tothe z axis, collimate the beams of the individual emitters of differentbars 1 a, 1 b, 1 c arranged one above the other and deflect the beam ofthe individual emitters, indicated in the drawings by 8, on the sameheight to the redirection element 5 such that the beams 8 of the emitterof a bar 1 a, 1 b, 1 c are separated. Preferably, gradient opticalcylinder lenses or multi-component cylinder lenses with sufficientisoplanacy are used as microcylinder lenses 2 a, 2 b, 2 c. Typical focallengths of the microcylinder lenses 2 a, 2 b, 2 c lie in the range of100 μm to approximately 1 mm.

The direction element 3 causes a deflection of the individual beams 8 ofthe emitters in the slow axis and a similar deflection of the beams ofall emitters of each individual bar in the fast axis such that the beams8 of the emitters of a bar 1 a, 1 b, 1 c meet at the same x position andthe central points of the beams of each bar meet at the same y positionon the redirection element 5.

Plano-convex or biconvex lenses or doublets, preferably with a largefield angle, with spherical or aspherical surfaces may be used as thedirection element 3

Another possible implementation provides for combinations of thesedirectional lenses 3 with prism arrays 9 according to FIGS. 3a-5 b,which cause a displacement of the beams 8 of the individual bars 1 a, 1b, 1 c on the redirection element 5 in the slow axis. Here, a prism 9 a,9 b, 9 c (not shown) is provided that deflects in the slow axis and isassigned to each bar 1 a, 1 b, 1 c. By way of the separation of thecentral points of the beams of the individual bars 1 a, 1 b, 1 c on theredirection element 5 thus achieved, a position of the focal spots foreach bar 1 a, 1 b, 1 c in the y direction can be individually achieved,provided that the redirection element 5 is appropriately constructed,for example, the individual focal spots can also be positioned preciselyon top of one another. Alternately, the combination of the directionlens 3 and the prism array 9 can be achieved by a dismantling of thedirection lens 3 into several segments arranged in the slow axisdisplaced relative to one another. The focal lengths of the directionelement 3 typically lie in the range of several mm to several 10 mm.

The redirection element 5 and the projection lens 4, 6 are locateddownstream of the direction element 3 (see FIG. 1). In the concreteimplementation, the lens 4, whose focal length corresponds to the focallength of the director, follows first. This first lens 4 of theprojection lens causes a collimation of the beam bundles of theindividual emitters in the slow axis. This allows an almostaberration-free operation of the redirection element 5. The embodimentoptions for the first lens 4 of the projection lens correspond to thevariants for the direction element 3.

The redirection element 5 comprises a number of elements stacked in thefast axis with a deflecting effect in the slow axis, for example, anarray of blazed gratings, a stack of prisms, or a mirror array. Afterthe redirection element 5, a collimated beam is obtained from each bar 1a, 1 b, 1 c with a right-angle or square cross-section. The beamdirection of this collimated beam from the redirection element 5 in thefast axis is different for each bar 1 a, 1 b, 1 c.

If a separation of the beams 8 of the individual bars 1 a, 1 b, 1 c isattained on the redirection element 5 in the slow axis by way of acombination of the direction lens 3 and the prism arrays 9 as in FIGS.3a-b and 5 a-b, these different beam directions can be compensated byappropriate elements 10 in the vicinity of the redirection element 5that deflect in the fast and slow axes. These elements 10 may beimplemented using, for example, additional prisms in the vicinity of theredirection element 5, using an appropriate construction of theredirection element 5, for example, as an array of two-dimensionaldeflecting blazed grating, or a combination of these elements. Thus,after the redirection element 5, an extensively symmetrical, collimatedbeam with a high radiance is present. For applications in which acollimated beam with a right-angular cross-section is needed, the secondlens 6 of the projection lens, which would otherwise follow here, may beomitted.

Conventionally, however, a focused exiting beam is needed. Thesubsequent lens 6 forms images of the individual emitters of therespective bar 1 a, 1 b, 1 c into one common focal spot.

Shown in FIG. 2 are the focal planes of the optic fibers 7 a, 7 b, 7 cassigned to the lens 6, into which the overlapping images of theemitters of each bar 1 a, 1 b, 1 c are coupled. By combining the opticcables 7 a, 7 b, 7 c into a fiber bundle 7, the desired symmetricalbundle cross-section with the greatest maintenance of radiance isattained.

If, as shown in FIGS. 3a-b and 5 a-b, the variant of the combination ofthe director lens 3 and the redirector 5, each with a prism array 9 or10, is realized, a common focal spot is achieved for all bars 1 a, 1 b,1 c in the focal plane of the lens 6. Thus, a spread fiber bundle forcombining the focal spots of the individual bars 1 a, 1 b, 1 c is notnecessary in this implementation.

What is claimed is:
 1. An optical arrangement for symmetrizing beamscomprising: a plurality of laser diodes arranged adjacent to oneanother; the plurality of laser diodes emitting beams which areasymmetrical relative to a first direction and a second direction, thesecond direction being perpendicular to the first direction; amicrocylinder lens optics arranged in an inclined manner about anoptical axis, whereby the beams emitted by the laser diodes in the firstdirection are collimated and deflected with different angles to beseparated; a direction element arranged downstream of the microcylinderlens optics, the direction element deflecting a beam of each individuallaser diode in the second direction, whereby each of the beams isdeflected at a different angle in the second direction, so that centralpoints of the individual beams converge at a predetermined distance inthe second direction, the direction element deflecting a beam of eachindividual laser diode in the first direction such that each of thebeams converges at a predetermined distance in the first direction; anda redirection element arranged at a predetermined distance downstream ofthe direction element, wherein the redirection element compensates fordifferent angles of deflection of the beams which are transmittedthrough the direction element in a plane.
 2. The arrangement of claim 1,wherein the plurality of laser diodes are arranged at least one of oneabove the other and on a common plane.
 3. The arrangement of claim 1,wherein the plurality of laser diodes are arranged in a fixed location.4. The arrangement of claim 1, wherein the plurality of laser diodes arearranged to form a laser diode stack.
 5. The arrangement of claim 1,wherein the optical axis corresponds to an assigned linear array oflaser diodes.
 6. The arrangement of claim 1, wherein the microcylinderlens optics comprises a plurality of microcylinder lenses.
 7. Thearrangement of claim 1, wherein the microcylinder lens optics hassufficient isoplanacy.
 8. The arrangement of claim 1, wherein theredirection element compensates for different angles of deflection ofthe beams transmitted through the direction element in a plane definedby the second direction and the optical axis.
 9. The arrangement ofclaim 1, wherein the first direction defines an “y” axis, wherein thesecond direction defines a “x” axis, and wherein the optical axisdefines a “z” axis.
 10. The arrangement of claim 9, wherein theredirection element compensates for different angles of deflection ofthe beams which are transmitted through the direction element in a planedefined by an x-z plane.
 11. The arrangement of claim 1, furthercomprising at least one projection lens arranged between the directionelement and the redirection element, whereby the at least one projectionlens directs the beams deflected in the second direction to a commonfocal spot.
 12. The arrangement of claim 11, further comprising at leastone optical fiber arranged at the common focal spot.
 13. The arrangementof claim 12, wherein the at least one optical fiber comprises one of aplurality of optical fibers and a fiber bundle.
 14. The arrangement ofclaim 1, wherein the microcylinder lens optics comprises a plurality ofmicrocylinder lenses, at least one of the plurality comprising one of agradient optical microcylinder lens, a spherical microcylinder lens, aaspherical microcylinder lens, and a Fresnel lens.
 15. The arrangementof claim 1, wherein the microcylinder lens optics comprises a pluralityof microcylinder lenses, each the plurality comprising at least one of agradient optical microcylinder lens, a spherical microcylinder lens, aaspherical microcylinder lens, and a Fresnel lens.
 16. The arrangementof claim 1, wherein the direction element comprises at least one of adoublet lens, a biconvex lens, a planoconvex lens.
 17. The arrangementof claim 16, wherein the direction element comprises spherical surfaces.18. The arrangement of claim 16, wherein the direction element comprisesaspherical surfaces.
 19. The arrangement of claim 1, further comprisingan optical element arranged adjacnt the direction element.
 20. Thearrangement of claim 19, wherein the optical element evenly deflects thebeams in the second direction.
 21. The arrangement of claim 19, whereinthe optical element comprise at least one of blazed gratings, a prismstack, and a mirror stack.
 22. The arrangement of claim 19, wherein theoptical element is sectioned and deflects the beams in the seconddirection.
 23. The arrangement of claim 1, wherein the redirectionelement comprises at least one of an array of blazed gratings, a prismstack, and a mirror stack.
 24. The arrangement of claim 1, furthercomprising an deflecting element arranged between the direction elementand the redirection element.
 25. The arrangement of claim 24, whereinthe deflecting element is arranged adjacent the redirection element,whereby the deflecting element deflects beams in the first directionsuch that they are emitted from the redirection element parallel to theoptical axis.
 26. The arrangement of claim 24, wherein the deflectingelement comprises at least one of an array of blazed gratings, a prismstack, and a mirror stack.
 27. The arrangement of claim 24, wherein thedeflecting element comprises a diffraction element.
 28. The arrangementof claim 1, wherein the redirection element comprises a diffractionelement.
 29. The arrangement of claim 1, further comprising a lenslocated between the direction element and the redirection element,whereby the lens causes a collimation of individual beams in the seconddirection.
 30. The arrangement of claim 29, wherein the lens is locatedadjacent the redirection element and comprises at least one of a doubletlens, a biconvex lens, and a planoconvex lens.
 31. The arrangement ofclaim 30, wherein the direction element comprises spherical surfaces.32. The arrangement of claim 30, wherein the direction element comprisesaspherical surfaces.
 33. The arrangement of claim 1, further comprisinga focusing lens arranged downstream of the redirection element, wherebythe focusing lens focuses the beams into at least one focus spot. 34.The arrangement of claim 33, wherein the focusing lens comprises atleast one of an achromate lens, an achromate and a meniscus lens, aplanoconvex lens, a planoconvex lens, a meniscus lens, and a biconvexlens.
 35. The arrangement of claim 34, wherein the focusing lenscomprises a spherical profile form.
 36. The arrangement of claim 34,wherein the focusing lens comprises an aspherical profile form.
 37. Anoptical arrangement for symmetrizing beams comprising: a plurality oflaser diodes emitting beams and arranged to form an array; a pluralityof microcylinder lenses adjacent the array; a direction element arrangeddownstream of the plurality of microcylinder lenses; the directionelement deflecting some beams in a first direction, whereby each of thebeams is deflected by a different angle in the first direction, suchthat central points of individual beams converge at a predetermineddistance in the first direction; the direction element deflecting somebeams in a second direction such that each of the beams converges at apredetermined distance in the second direction; and a redirectionelement arranged at a distance downstream the direction element, whereinthe redirection element compensates for different angles of deflectionof the beams transmitted through the direction element.
 38. An opticalarrangement for symmetrizing beams comprising: a plurality of laserdiodes emitting beams and arranged to form an array; a plurality ofmicrocylinder lenses adjacent the array; a direction element arrangeddownstream of the microcylinder lenses; the direction element deflectingsome beams in a first direction, whereby each of the beams is deflectedby a different angle in the first direction, such that central points ofindividual beams converge at a predetermined distance in the firstdirection; the direction element deflecting some beams in a seconddirection such that each of the beams converges at a predetermineddistance in the second direction; a redirection element arranged at adistance downstream of the direction element; at least one lens arrangedadjacent the redirection element; and at least one optical fiberarranged downstream the redirection element and the at least one lens,wherein at least some of the beams exiting the redirection element aredirected to a common focal spot on the at least one optical fiber.